1. Field of the Invention:
This invention relates generally to earth-boring bits, lubricated with a system that includes a hydrostatic pressure compensator to balance the internal pressure of the lubricant inside the bit with the hydrostatic pressure of a liquid drilling fluid that surrounds the bit during drilling. In this combination the invention relates to a metal face seal assembly.
2. Description of the Prior Art:
The first successful cantilevered rolling cutter bit invented by Howard R. Hughes, Sr., U.S. Pat. No. 930,759, did not have an effective seal but nonetheless utilized a piston type pressure lubricator that urged a heavy grease into a friction or journal bearing. Because the grease was expended too rapidly, sealed bearing designs were eventually abandoned in favor of unsealed bits with anti-friction, ball and roller bearings that were unlubricated. Such bits were commercially successful in the '40s and in the '50s, lasting into the '60s when Gerald O. Atkinson et al perfected the first seal useful for relatively long periods in retaining lubricant in the anti-friction bearings, as disclosed in U.S. Pat. No. 3,075,781.
Because a friction or journal bearing has greater load carrying capacity than an anti-friction bearing, its potential was not forgotten and was unlocked in the late 1960's by Edward M. Galle, who provided an O-ring sealed journal bearing combination that sometimes lasted twice as long as anti-friction bearings in the hard, slow drilling of West Texas. (See U.S. Pat. No. 3,397,928.) This bit became predominant in the marketplace, but the O-ring seal has limitations that prevented it from being the final solution to the puzzle of sealing rock bit bearings.
U.S. Pat. No. 4,516,641 of Bruce H. Burr discloses the first commercially successful rock bit which utilizes a metal face seal. In this bit the seal assembly acts as a secondary compensator, being free to move axially in the seal groove to limit pressure buildup in the lubricant behind the seal caused by the rapid movement of the cutter on the bearing shaft.
The prior art recognizes an advantage in preventing the rotation of a Bellville and certain other seals by press fit, adhesives, staking or the use of an abutment. (See U.S. Pat. No. 3,680,873 and the prior art referred to therein.) One attempt to prevent rotation of a metal face seal relative to the bearing shaft is to roughen the seal groove by particulate blasting to increase the coefficient of friction between the metal and a resilient portion of the seal. If rotation occurs, the roughened surface may result in an accelerated deterioration of the resilient member and a consequent loss of sealing effectiveness.